It is in fact known that the electric and magnetic components of the field created by an electromagnetic source as functions of the time or of the pulsation, such as observed on the surface of the ground, are connected to electromagnetic characteristics (conductivity, permeativity, magnetic permeability) of media placed under the influence of this field. These characteristics depend themselves on the nature of the sub-soil. From this, deduction of the structure and nature of the sub-soil from observation of electromagnetic field have for a long time been sought.
The present fields of application of sub-soil analysis extend to the general study of the earth (Physics of the Globe), to stratum research (mineral and hyrocarbon) and to civil engineering.
Numerous methods of acquisition and of processing of the measurement of electrical and magnetic components of the field have already proposed.
However in the general manner the methods proposed to data have not given full satisfaction.
In particular, the main methods of acquisition and processing do not permit separation correctly of the useful signal, connected to the source of data, from signals due to other sources (the noise). Nevertheless the quality of the result obtained (estimation of the structure and of the composition of the sub-soil, for example) depend on the quality of the processed signal.